AVOIDING INTERFERENCES FROM GOODS-BUFFERS - A CONTIGUOUS SERIES OF NONCOMPLEXING TERTIARY AMINE BUFFERS COVERING THE ENTIRE RANGE OF PH-3-11

Of the 20 well-known buffers proposed by Good, all but 3 form metal io n complexes which can result in serious interferences, particularly in protein analyses. The structural features responsible for such comple x formation have been identified. Based on a mechanistic analysis of t he metal complexation process, it is proposed that tertiary amine comp ounds, having N-substituents which are ethyl or larger, are sterically inaccessible for initial bond formation with solvated metal ions in a queous solution. Thus, in the absence of donor atoms on the alpha-, be ta-, or gamma-carbons, metal complexation cannot proceed. The proposed noncomplexing compounds include Good's 3 noncomplexing buffers (Mes, Mops, Pipes) plus six related species. Mixed-mode acid dissociation co nstants (hydrogen ion in terms of activity, conjugate acid-base specie s in molar concentrations) have been determined for all compounds in t heir protonated form at 25 degrees C, mu = 0.10 M (NaNO3). The values for four compounds in this series are reported here for the first time : viz., N,N'-diethylpiperazine for which log K-a1(m) = 4.67 +/- 0.03 a nd log K-a2(m) = 8.83 +/- 0.02; N,N,N',N'-tetraethylmethylenediamine f or which log K-a1(m) < 1 and log K-a2(m) = 11.01 +/- 0.03; ,N'-diethyl -N,N'-bis(3-sulfopropyl)ethylenediamine for which log K-a1(m) = 5.75 /- 0.03 and log K-a2(m) = 9.37 +/- 0.02; and piperazine-N,N'-bis(2-eth anesulfonic acid) (Pipes) for which log K-a1(m) = 2.81 +/- 0.01 (the v alue of log K-a2(m) having been previously reported). (C) 1997 Academi c Press.